1. Field of the Invention
The invention in general relates to high power microwave devices.
2. Description of Related Art
In the field of microwave electronics a need exists for a high power, high frequency transistor. A widely used transistor for this purpose is the GaN (gallium nitride) based HEMT (high electron mobility transistor). The HEMT is a transistor which has a heterojunction formed between two semiconductor materials of different bandgaps. Current in such a device is confined to a very narrow channel at the junction, such current being known as a 2DEG (two dimensional electron gas).
Although the GaN based HEMT has many advantages over a GaAs (gallium arsenide) based HEMT it has several problems, one of which is the requirement for a prohibitively high substrate expense. That is, due to the thermal conductivity requirements of high power applications, SiC (silicon carbide) is used as the substrate for the layers comprising the HEMT.
A typical HEMT is structurally similar to a conventional, generally planar, field effect transistor and a particular insulating SiC substrate must be used. Such substrate can be an order of magnitude higher in cost than the widely used n+ SiC.
Accordingly, it would be desirable to have a HEMT type device which may be fabricated on an n+ SiC substrate thereby benefiting not only from the reduced substrate cost, but a higher device yield, due to the superior quality of n+ SiC substrates. It is a primary object of the present invention to provide such device.